This invention relates to optical switches and in particular to an optical switch having a plurality of switching positions.
In optical communication systems it is often necessary to switch an optical signal between different optical paths, be it along an optical waveguide such as an optical fiber, or in free space. Optical switching devices may generally be classified into moving-beam switches and moving-fiber switches. Moving-beam switches redirect the optical signal path between stationary waveguides or in free space. Moving-fiber switches physically change the location of optical fibers to be switched.
Different categories of optical switches for switching optical signals include electrical switches, solid-state switches, mechanical switches, and optical switches and combinations therebetween.
Electrical switches convert an optical signal to an electrical signal and then switch the electrical signal by conventional switching techniques. Electrical switches then convert the electrical signal back into an optical signal. Electrical switches are faster then existing mechanical switches but are also significantly more expensive. Furthermore, electrical switching of optical signals is bandwidth limited since a converted electrical signal can not carry all the information in an optical signal. This bandwidth limitation of electrical switches severely limits the advantages of using fiber optics.
Solid-state optical switches have fast switching speeds and the same bandwidth capacity as fiber optics. However, the cost for solid-state optical switches is 30 to 100 times more than those for existing mechanical switches. Another disadvantage of solid-state optical switches is that they incur insertion losses exceeding 20 times those for existing mechanical optical switches.
Mechanical optical switches are typically lower in cost than electrical or solid-state optical switches, provide low insertion loss, and are compatible with the bandwidth of fiber optics
The activation mechanism used in the optical deflection switch of the present invention is a moving-beam switch mechanism.
An exemplary optical fiber switch that utilizes a moving mirror to perform the switching function is disclosed by Levinson in U.S. Pat. No. 4,580,873 issued Apr. 8, 1986 which is incorporated herein by reference. Although this invention appears to adequately perform its intended function, it is believed too costly and somewhat complex.
There have been several designs of optical deflection switches using Frustrated Total Internal Reflection (FTIR) to accomplish switching or modulation of an optical signal. In almost all cases these systems begin with air gap which produces total internal reflection, and then rapidly drives the material to less than one tenth wavelength spacing to produce frustrated total internal reflection. Such systems are disclosed in U.S. Pat. Nos. 4,249,814; 3,649,105; 3,559,101; 3,376,092; 3,338,656; 2,997,922; and 2,565,514. In all of these systems there is a problem in overcoming friction and damage to the glass.
Another exemplary moving-beam optical switch that redirects the optical signal path between stationary waveguides is disclosed in U.S. Pat. No. 5,444,801 to Laughlin incorporated herein by reference. The invention described therein teaches an apparatus for switching an optical signal from an input optical fiber to one of a plurality of output optical fibers. This apparatus includes means for changing the angle of the collimated beam with respect to the reference so that the output optical signal is focused on one of the plurality of output optical fibers. Similar mechanical optical switches are disclosed in
U.S. Pat. Nos. 5,647,033; 5,875,271; 5,959,756; 5,555,558; 5,841,916; and 5,566,260 to Laughlin incorporated herein by reference.
Laughlin teaches switching of optical signals between input fibers and output fibers through shifting of one or more virtual axis of the system by changing the position of a second reflector between multiple positions. This second reflector has a wedge shape to change the angle of the collimated beam by a selected amount to direct the beam to different output locations. However, the output locations are all lying along a diameter in the output focal plane of the GRIN lens as shown in FIG. 1.
Another optical switch based on total internal reflection is described in U.S. Pat. No. 4,988,157 in the name of Jackel et al. issued January 1991. This patent teaches the use of changing the refractive index of a region by providing electrodes positioned adjacent slots which are selectively activated to electrolytically convert the fluid to gaseous bubbles, thereby destroying the index matching across the slot and causing light to be reflected by the slot rather than propagating across the slot. In the presence of a catalyst, a pulse of opposite polarity or of sufficient size and of the same polarity will destroy the bubble. Although Jackel""s invention appears to achieve its intended function, it is complex and costly to manufacture.
As of late, monolithic waveguiding devices have gained popularity. These devices tend to be compact and cost effective to manufacture. Such devices are described by the applicant in U.S. Pat. No. 5,470,692 entitled Integrated optic components issued Nov. 28, 1995. In the ""692 patent an integrated optic component comprises a substrate carrying a layer of polymeric material. The component may be poled so as to be an active component and may be in the form of a ridge guide.
Many monolithic devices having, for example polymer waveguides disposed therein provide a single guided mode, similar to single mode optical fibre. Another class of monolithic waveguiding devices are comprised of waveguides disposed in glass wherein an ion diffused region or a reactive-ion-etched structure overcoated with a cladding can serve as a waveguide core.
Polymer waveguides disposed on a substrate offer some advantages over inorganic glass such as silica, however, low levels of signal loss i.e. high transparency of inorganic glass is desirable and preferred to polymer. Polymer waveguides are noted for low transparency, i.e. significant loss; polymer waveguides have a high co-efficient of expansion and, associated with that a high (negative) thermo-optic co-efficient, and a low thermal conductivity. In contrast, inorganic glass has a high transparency, a high thermal conductivity, and a low (positive) thermo-optic coefficient.
This invention utilizes these differences in the two materials in a synergistic manner by providing an inorganic glass/polymer hybrid core structure that highly advantageous.
Typically, optical fibers comprise a light-carrying core, for example an inorganic glass such as fused silica or a polymer such as polymethyl methacrylate, and a cladding material having a lower refractive index than the core. The cladding material serves to confine the light energy within the core and thereby allows propagation of light by a phenomenon generally known as xe2x80x9ctotal internal reflection.xe2x80x9d
It is an object of this invention, to provide a waveguide that uses the beneficial characteristics of inorganic glass such as silica, and as well the beneficial characteristics of polymer waveguides, while minimizing the unwanted characteristics of these materials.
For example, it is desired to have a optical waveguide with an active region which is highly thermo-optic active, so that it may be switched, or modulated with low power. Notwithstanding, it is desired to have an optical waveguide that under normal transmission is highly transparent, i.e. has little signal power loss. Yet still further, it is desired to have a waveguide wherein the refractive index can be changed relatively efficiently and significantly with minimal power. And yet still further, it is desired to have a waveguide with two different regions, having guided light transmitting cores that have relatively different refractive indices, yet that can be modified by the application of a suitable energy, to increase the refractive index difference between the two regions.
It is an object of this invention, to provide a waveguide that uses the beneficial characteristics of inorganic glass such as silica, and as well the beneficial characteristics of polymer waveguides, while minimizing the unwanted characteristics of these materials.
It is an object of this invention to provide an optical switch that requires low power.
In accordance with the invention there is provided, an optical switch comprising: a first waveguide having a first core of a first material having a first input end and a first output end; and a second waveguide having a second core of the first material having second input end and a second output end, the first input end being spaced from the second input end by a distance d2, and a coupling region between the first input end and the first output end, wherein the first and second waveguide cores are very closely spaced by a distance d1, wherein d1 less than  less than d2; and a second material contacting the first and second waveguide cores in the coupling region, the second material being different than the first material; and, means for providing a refractive index difference between the first and second materials to providing switching of light launched into one of the input ports.
In accordance with the invention there is further provided, an optical switch comprising two waveguides having separate cores that together form an X pattern, the cores being close together at an active region where they converge and the cores diverging outward therefrom, the cores having a region of a different material disposed therebetween and contacting therewith, and means for changing a refractive index difference between the different material region and the cores.
This invention is not limited to waveguides having a core of a particular shape, however this invention is related to waveguides formed of materials having different optical properties contiguously disposed one beside the other.
Instead of switching by thermal means as described in a preferred embodiment hereafter, switching can be achieved by applying a voltage to vary the refractive index if an electro-optic polymer is used, or compression may be used as a means of varying the polymers refractive index and providing an index difference between the polymer and adjacent glass region.